1. Field of the Invention
The present invention relates to an active matrix display device.
2. Description of the Related Art
In liquid crystal display device that is one of active matrix devices, substrates that are opposed to each other with a liquid crystal interposed in between are used as a container and an area that extends parallel with the liquid crystal and where a number of pixels are arranged serves as a display area.
Active matrix display devices are such that the regions enclosed by gate signal lines that extend in the x direction and are arranged in the y direction and drain signal lines that extend in the y direction and are arranged in the x direction are made pixel regions. Each pixel region is provided with a thin-film transistor that is driven being supplied with a scanning signal from a gate signal line on one side and a pixel electrode that is supplied with a video signal from a drain signal line on one side via the thin-film transistor. All of the above components are formed by film forming technologies.
Further, there are known active matrix display devices of a type in which a gate signal line driving circuit for supplying scanning signals to the gate signal lines and a drain signal line driving circuit for supplying video signals to the drain signal lines are formed by film forming technologies in regions other than the display area on a substrate on which the thin-film transistors are formed.
The above gate signal line driving circuit and drain signal line driving circuit includes a number of inverters that are formed by thin-film transistors configured in the same manner as the above-mentioned thin-film transistors, and hence it is an ordinary procedure to form those driving circuits and the pixels in parallel.
However, in active matrix display devices of the above type, it is pointed out that the gate signal line driving circuit and the drain signal line driving circuit occupies large areas, as a result of which the distance between the outline of the display area and that of a transparent substrate (i.e., a frame width) becomes long.
The present invention has been made in view of the above circumstances in the art, and an object of the invention is therefore to provide a active matrix display device in which the integration densities of the gate signal line driving circuit and the drain signal line driving circuit are increased.
Representative parts of the invention will be described below briefly.
The invention provides an active matrix display device comprising a substrate having a display area including a set of pixel regions each having a first thin-film transistor; and a driving circuit forming area located outside the display area and having second thin-film transistors, wherein a gate electrode of the first thin-film transistor is made of a material different than a gate signal line and has a portion that is electrically connected to the gate signal line; a gate electrode of each of the second thin-film transistors is made of a material different than a wiring layer or electrode to be connected to it and has a portion that is electrically connected to the wiring layer or electrode; the gate electrode of the first thin-film transistor is made of the same material as that of each of the second thin-film transistors; and the gate signal line is made of the same material as the wiring layer or electrode.
The gate electrode of the first thin-film transistor and/or each of the second thin-film transistors may be laid directly or indirectly on or under the gate signal line.
The gate electrode of the first thin-film transistor and/or each of the second thin-film transistors may have a portion that is formed with a material the same as or different than the gate signal line in a layer different than the gate signal line.
In the above active matrix display device, the gate electrode of each second thin-film transistor formed in the driving circuit forming area is connected to another wiring layer or electrode in such a manner as to be directly laid on or under the latter without intervention of a contact hole.
Therefore, there is no need for securing space for formation of a contact hole, making it possible to narrow the driving circuit forming area.
With the above configuration, the threshold voltages of the first thin-film transistors in the respective pixel regions and the second thin-film transistors can be equalized by giving those two kinds of thin-film transistors the same structure (forming their gate electrodes with the same material).